gistfile1.txt

@Injectable({providedIn: ServiceModule})
export class Service {}

@NgModule({}) export class ServiceModule {}

@NgModule({
  imports: [ServiceModule]
})
export class AppModule {}

@Component({})
export class Cmp {
  constructor(svc: Service) {}
}

gistfile2.txt

providers: [Service]

1) telling Angular which injector should create the service
2) actually registering the service with the injector
3) specifying when the service should be loaded (in terms of
   lazy loading)

gistfile3.txt

export interface IService {
}

export const SERVICE_TOKEN = new InjectionToken<IService>({
  providedIn: 'root',
  factory: () => inject(ServiceImpl)
});

// useValue: foo
factory: () => foo,
// useExisting: SomeToken
factory: () => inject(SomeToken)
// useClass: SomeClass
factory: () => new SomeClass(inject(DepA), inject(DepB)),
// useFactory: factoryFn, deps: [DepA, DepB]
factory: () => factoryFn(inject(DepA), inject(DepB))



//{provide: SERVICE_TOKEN, useClass: ServiceImpl}